Feed assembly for circular or linear polarization



March 6, 1962 A. w. MOELLER ET AL 3,024,463

FEED ASSEMBLY FOR CIRCULAR OR LINEAR POLARIZATION Filed Oct. 16, 1958 INVENTORS ALVIN W. MOELLER JOHN G. NEUBERTH ATTORNE S United States Patent 3,024,463 FEED ASSEMBLY FOR CIRCULAR 0R LINEAR POLARIZATION Alvin Moeller, Towson, and John G. Neuberth,

Timomum, Md, assignor to The Bendix Corporation,

Towson, Md., a corporation of Delaware Filed Oct. 16, 1958, Ser. No. 767,530 6 Claims. (Cl. 343-783) This invention relates to a feed mechanism by means of which microwave energy may be translated between a feed horn and a rectangular waveguide. The mechanlsm may, at the will of the operator, translate energy which is either linearly or circularly polarized at the feed horn. With either polarization at the feed horn the wave is linearly polarized at the rectangular waveguide.

Mechanisms for accomplishing the above results have been known but they are of excessive size, weight and cost and are not readily tunable.

It is an object of the invention to provide a feed assembly capable of handling either linearly or circularly polarized energy which is considerably more compact and, consequently, of less weight and cost than previously known devices for this purpose.

It is another object of the invention to provide a feed assembly of this type in which both the amplitude and phase of the circularly polarized energy may readily be adjusted.

These and other objects and advantages of the invention are realized in an assembly comprising a single step quarter-Wave transformer for transforming energy from the TE mode in the rectangular Waveguide to a TE mode in a circular waveguide, an orthogonal mode generator for the circular waveguide and a phase shifting feed horn receiving the energy from the circular waveguide. The orthogonal mode generator comprises a series of disc-like sections with each section having a coaxial circular opening extending through it. These openings together form a circular waveguide. Extending transversely across each opening is a mode aligning rod. Means are provided to rotate a first of the sections through a 45 angle from a first position to a second, a pin and slot connection is provided between the first and second sections, and between the second and third sections, such that when the first section is in its first position all the rods are parallel, and when it is moved to its second position the second section is rotated by 30 and the third by 15. A differential phase shifting means is provided in the feed horn.

In the drawing:

FIG. 1 is a side elevational view of a feed assembly embodying the invention, with a portion of the casing cut away;

FIG. 2 is a front elevational view of the assembly of FIG. 1;

'FIG. 3 is an exploded view, in perspective, of the assembly of FIG. 1;

FIG. 4 is a graph showing the electric field vectors existing, at various points in the assembly of FIG. 1, in the energy flowing therethrough;

FIG. 5 is an elevational view of a fragment of the disc 14 showing the rear face thereof; and,

FIG. 6 is an elevational view of the disc 16 showing the rear face thereof.

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Referring now more particularly to the drawing, there is shown an assembly comprising a housing 1 having a front plate 2 and a back plate 3. The back plate has formed therein in a central location a rectangular aperture 4.

The front plate 2 has formed therein a square aperture 5 coaxial with the aperture 4 in the back plate. The thickness of the back plate and the front plate in the portions there-of surrounding the apertures is that of a quarter-wave length of the center frequency of the energy band intended to be translated by the assembly. Secured to the outside of the front plate is a feed horn 6. The base of the feed horn has formed therein a square aperture matching the aperture 5. The horn is rectangular in cross-section throughout its length and flares out wardly in both dimensions from the portion 7, which is attached to the front plate. Located within the horn near the portion 7 is a horizontally disposed dielectric slab 8. The slab is mounted on a pair of horizontally extending rods 9, the ends of which extend through the sides of the feed horn and are supported by a square yoke 10 surrounding the horn. An adjusting screw 11 is provided for adjusting the positioning of the yoke vertically with respect to the feed horn, thus adjusting the position of the slab within the feed horn. A pair of matching stubs 12 extend inwardly from the vertical sides of the feed horn along the horizontal plane of symmetrythereof. Also located in the horizontal plane of symmetry in the mouth of the horn is a septum 13.

Contained within the housing 1, between the front and back plates, are three discs 14, 15 and 16. The central portions of these discs have a thickness which is equal to a quarter-wavelength of the center frequency of the energy to be translated. When the discs are assembled these portions are in contacting relationship with each other and with the central portions of back plates 2 and 3. Formed coaxially with each of the discs is a circular aperture extending therethrough and forming a circular waveguide when the discs are assembled. Extending across the aperture in the central plane of each of the discs is a rod 17. The disc 15 has extending from each face of its central portion a pin 18, only one of which is visible in 'FIG. 3. The end of one of these pins extends into a slot 19 formed in the adjacent face of the central portion of the disc 16. The end of the other pin extends into a similar slot 20 formed in the abutting face of the central portion of the disc 14.

The periphery of the face of the central portion of disc 14, which faces the disc 15, is toothed to form a gear 21. Meshing with the gear 21 is a gear 22 mounted on a shaft 23, extending through the upper portion 24 of the housing above the back plate 3, and terminating'in a lever 25. A pin 26 extends from the front face of the gear 22 near the periphery thereof and a pair of pins 27 and 28 extend inwardly from the front plate 2 of the assembly, these latter pins being equally spaced from the horizontal plane containing the axis of the shaft 23. Extending between the pin 27 and the pin 26 is one leg 29 of a V-shaped coil spring, the other leg 30 of which extends between the pins 26 and 28.

The inwardly directed face of the back plate 3 is formed with an annular recess 31 surrounding the central portion thereof. Extending upwardly from the base of the back plate into this annular recess are a pair of pins 32 and 33, the lower portions of which are threaded and extend through threaded holes formed in the back plate. The rearwardly directed face of the disc 16 has formed on its central portion, near the periphery thereof, a pair of oppositely located shoulders 34 and 35 against which the ends of the pins 32 and 33 abut.

In the operation of the above described device there is intended to be secured to the exposed face of the back plate 3 a standard rectangular waveguide in which energy is excited in the TE mode. The aperture of the waveguide matches in location the aperture formed in the back plate and the joining portions of the Waveguide and the back plate are provided with conventional annular choke recesses to minimize losses. The aperture 4 is dimensioned in accordance with known practice to act as a transformer to transform the energy from the TE mode in the rectangular guide to a TE mode in the circular guide made up by the apertures 50 in the discs 14, 15 and 16. For this purpose the wide cross-sectional dimension of the aperture 4 will be the same as that of the rectangular guide, but the narrow cross-sectional dimension will be longer than that of the rectangular guide and the corners of the aperture 4 are rounded.

When the assembly is in the condition shown in FIG. 3 with the lever 25 in its lefthand position the rods 17 in the three discs will extend in mutual parallelism and the energy proceeding through the apertured discs will maintain its linear polarization, since the rods are parallel to the wide dimension of the rectangular waveguide. The spring composed of legs 29 and 30 acts as an over center snap action device tending to retain the lever 25 in either of its extreme positions. These extreme positions are determined by the positions of the pins 32 and 33 which are adjustable by means of conventional screw driver slots formed in the ends thereof. When the lever is in its lefthand position the angular positions of the discs 14, 15 and 16 will be determined by the pin 32 coming in contact with the shoulder 34 formed on the disc 16, and also by the coaction of the pins 18 with the ends of the slots 19 and 20 formed in the discs 14 and 16.

The square aperture with its rounded corners acts as a transformer to transform the TB energy of the circular guide back into the TE mode in the feed horn. Since the dielectric slab 8 and the septum 13 in the feed horn are perpendicular to the electric vector of the energy in this mode, the wave will not be affected thereby. The reactances of the horns formed by the septum 13 are matched by means of the capacitive pins 12 so as not to effect the radiation pattern.

When the lever 25 is moved to its righthand position the discs 14, 15 and 16 will be rotated and will come to rest in positions dictated by the coaction of the end of pin 33 with shoulder 35 and the coaction of the pins 18 with the slots 14 and 16. The slots are so dimensioned and located that rotation of the lever to its righthand position, as seen in FIG. 3, will rotate the disc 14 by 45. At the end 6% 15 of this rotation the disc 15 will be picked up and will be rotated through 30. At the end of 15 of the rotation of disc 15 the disc 16 will be picked up and will be rotated until its shoulder 35 contacts the end of the pin 33.

As shown in FIG. 4 the electric vector of the energy in discs 14, 15 and 16 will, since it remains perpendicular to the rods 17, have been rotated through 45, 30 and 15, respectively, in the three discs. This is indicated by the graphs 40, 41 and 42 of FIG. 4. The graph 43 indicates the direction of the electric vector in the aperture 4, while graph 44 indicates its direction in the rectangular waveguide connected to the rear face of back plate 3.

The electric wave now enters the square aperture 5 from the disc 14 at a 45 angle to the guide walls and can be considered to be composed of two components in the TE mode with their electric vectors mutually perpendicular, as indicated by the graph 45 of FIG. 4. It will retain this condition as it enters into the base portion 7 of the feed horn. Since the horn 6 flares out it provides approximately 20 of differential phase shift to the two waves. A circularly polarized wave is one in which two equal amplitude waves which are out of time and space phases are present and to achieve this condition an additional 70 of differential phase shift must be supplied by the dielectric slab 8 in the square portion of the horn. This phase shift can be obtained by adjusting the vertical position of the slab 8 by means of the screws 11 on yoke 10. Moving the slab 8 toward the center of the guide increases the differential phase shift. The ends of this slab are tapered to give a minimum mismatch. The effect of the slab is indicated in FIG. 4 by the graph 46, while the addition of 20 shift provided by the tapered horn 6 produces the result indicated by graph 47.

The angular adjustment of sections 14, 15 and 16 determines the magnitude of the horizontal and vertical electric field vectors which propagate through the aperture 5. As section 14 is rotated from the linear polarization position toward the circular polarization position, the vertical electric component decreases and the horizontal electric component increases. The pin 33 may be set to achieve equality between the horizontal and vertical electric vectors for the circular polarization position.

In some applications it may be desirable to utilize elliptical polarization. This condition can be achieved by adjusting pin 33 to obtain the requisite relative magnitudes between the horizontal and vertical electric vectors while the position of slab 8 can be adjusted to obtain the required phase shift therebetween.

If an antenna is to be circularly polarized the horn patterns should be the same regardless of polarization. This is not possible with a conventional horn since it will be noted that, for a given aperture, the beamwidth will be wider if the aperture is in the magnetic plane than if it is in the electric plane. The septum 13 acts as a polarization compensating means. The septum has virtually no effect on the energy when the electric wave is perpendicular to it, as has been stated. However, for the electric vector which is parallel to the septum 13 the conductive nature thereof, in effect divides the horn into two equal side-by-side apertures and equalizes the horn patterns for the two components of the polarized energy.

Conventional annular choke joint recesses are formed in the coacting surfaces of the discs 14, 15 and 16 and the front and back plates 2 and 3 to minimize losses.

It is evident that other means than that shown can be used to move the discs between their positions of rest. They may, for example, be motor driven.

What is claimed is:

1. A feed mechanism for translating radio frequency energy between two points at one of which it exists in a linearly polarized state and at the other of which it is linearly polarized and either parallel or inclined 45 relative to the energy at said one point at the will of an operator, comprising: a circular waveguide formed of a plurality of rotatably joined sections each having a length equal to an integral number of quarter-wavelengths at the center frequency of the band of frequencies to be translated by said mechanism, means coupling the energy at said one point into one end of said waveguide in the T13 mode, mode aligning means in each of said sections, means for coupling the energy out of the other end of said waveguide, and means operable to rotate said sections between two positions of rest, in one of which said mode aligners are so positioned that the electric vectors of the waves existing in said sections and at said one point lie in the same plane and in the other of which the electric vector of the one of said sections nearest said one point is separated from the electric vector of the wave existing at said point by an angle equal to 45 divided by the number of said sections, the electric vector of the wave existing in each succeeding one of said sections being separated in the same rotational sense from that of the preceding section by the same angle.

2. An antenna and feed mechanism for translating radio frequency energy between two points at one of which it existsin a linearly polarized state and at the other of which it may either be linearly or circularly polarized at the will of an operator, comprising: a circular waveguide formed of a plurality of sections each having a length equal to an integral number of quarterwavelengths at the center frequency of the band of frequencies to be translated by said mechanism, means coupling the energy at said one point into one end of said waveguide in TE mode, mode aligning means in each of said sections, a feed horn having a throat of square cross-section, means coupling the energy in said waveguide into said throat in the TE mode, means operable to rotate said sections between two positions of rest, in one of which said mode aligners are so positioned that the electric vectors of the waves existing in said sections and at said one point lie in the same plane and in the other of which the electric vector of the one of said sections nearest said one point is separated from the electric vector of the wave existing at said point by an angle equal to 45 divided by the number of said sections, the electric vector of the wave existing in each succeeding one of said sections being separated in the same rotational sense from that of the preceding section by the same angle, whereby the energy coupled into said throat consists of two components the electric vectors of which are orthogonal, and means in said horn imparting a differential phase shift of 90 to the energy of said components.

3. An antenna and feed mechanism for translating radio frequency energy between two points at one of which it exists in a linearly polarized state and at the other of which it may either be linearly or circularly polarized at the will of an operator, comprising: a circular waveguide formed of a plurality of sections each having a length equal to an integral number of quarter wavelengths at the center frequency of the band of fre quencies to be translated by said mechanism, means coupling the energy at said one point into one end of said waveguide in the TE mode, mode aligning means in each of said sections, a feed horn having a throat of square cross-section, means coupling the energy in said waveguide into said throat in the TE mode, means operable to rotate said sections between two positions of rest, in one of which said mode aligners are so positioned that the electric vectors of the waves existing in said sections and at said one point lie in the same plane and in the other of which the electric vector of the one of said sections nearest said one point is separated from the electric vector of the wave existing at said point by an angle equal to 45 divided by the number of said sections, the electric vector of the wave existing in each succeeding one of said sections being separated in the same rotational sense from that of the preceding section by the same angle, whereby the energy coupled into said throat consists of two components the electric vectors of which are orthogonal, means in said horn imparting a differential phase shift of 90 to the energy of said components, and a polarization compensating septum in the mouth of said horn, said septum being perpendicular to the plane containing the electric vectors of the wave existing in said sections when they are in said one position of rest.

4. A feed mechanism for translating radio frequency energy between two points at one of which it exists in a linearly polarized state and at the other of which it is linearly polarized and either parallel or inclined 45 relative to the energy at said one point at the will of an operator, comprising: a circular waveguide formed of a plurality of rotatable sections each having a length which is an integral number of quarter wavelengths at the center frequency of the band of frequencies to be translated by said mechanism, means coupling the energy at said one point into one end of said waveguide in the TE mode, mode aligning means in each of said sections, means for coupling the energy out of the other end of said waveguide, and means operable to rotate said sections between two positions of rest, in one of which said mode aligners in said sections extend in mutual parallelism and lie in a plane perpendicular to the electric vector of the wave existing at said one point and in the other of which the mode aligner in the one of said sections nearest said throat is rotated by 45, the mode aligners in the remainder of said sections being rotated by lesser amounts such that equal angular separations in the same rotational sense exist between the electric vectors of the waves in adjacent sections and between the electric vectors of the wave existing at said one point and in the one of said sections nearest said one point.

5. An antenna and feed mechanism for translating radio frequency energy between two points at one of which it exists in a linearly polarized state and at the other of which it may be either linearly or circularly polarized at the will of an operator, comprising: a circular waveguide formed of a plurality of rotatable sections each having a length which is an integral number of quarter wavelengths at the center frequency of the band of frequencies to be translated by said mechanism, means coupling the energy at said one point into one end of said waveguide in the TB mode, mode aligning means in each of said sections, a feed horn having a throat of square cross-section, means coupling the energy in said waveguide into said throat in the TE mode, means operable to rotate said sections between two positions of rest, in one of which said mode aligners in said sections extend in mutual parallelism and lie in a plane perpendicular to the electric vector of the wave existing at said one point and in the other of which the mode aligner in the one of said sections nearest said throat is rotated by 45 the mode aligners in the remainder of said sections being rotated by lesser amounts such that equal angular separations in the same rotational sense exist between the electric vectors of the waves in adjacent sections and between the electric vectors of the wave existing at said one point and in the one of said sections nearest said one point, whereby the energy coupled into said throat consists of two components the electric vectors of which are orthogonal, and means in said feed horn imparting a differential phase shift of to the energy of said components.

6. An antenna and feed mechanism for translating radio frequency energy between two points at one of which it exists in a linearly polarized state and at the other of which it may be either linearly or circularly polarized at the will of an operator, comprising: a circular waveguide formed of a plurality of rotatable sections each having a length which is an integral number of quarter-wavelengths at the center frequency of the band of frequencies to be translated by said mechanism, means coupling the energy at said one point into one end of said waveguide in the TE mode, mode aligning means in each of said sections, a feed horn having a throat of square cross-section, means coupling the energy in said waveguide into said throat in the TE mode, means operable to rotate said sections between two positions of rest, in one of which said mode aligners in said sections extend in mutual parallelism and lie in a plane perpendicular to the electric vector of the wave existing at said one point and in the other of which the mode aligner in the one of said sections nearest said throat is rotated by 45, the mode aligners in the remainder of said sections being rotated by lesser amounts such that equal angular separations exist in the same rotational sense between the electric vectors of the waves in adjacent sections and between the electric vectors of the wave existing at said one point and in the one of said sections nearest said one point, whereby the energy coupled into said throat consists of two components the electric vectors of which are orthogonal, means in said feed horn imparting a differential phase shift of 90 tothe energy of said components, and a polarization compensating septum in the mouth of said feed horn, said septum being parallel to the plane containing said mode aligners when vsaid sections are in said one position of rest.

References Cited in the file of this patent I UNITED STATES PATENTS 1-' Fox Mar. 23, 1948 Y, .Purcell Aug. 19, 1952 Zaleski Feb. 10, I953 HershfieId July 24, 1956 Crawford et al. Oct. 22, 1957 Fitzmorris Mar. 24, 1959 

